Eddystone EB35. FM mod. - UK Vintage Radio Repair and Restoration Discussion Forum

crestavega · 6th Jan 2020, 2:03 pm

Has anyone got any practical experience of the FM IF mod on the EB35 Mk1?
'Ive acquired one, which I assume to be original (ie, unmodded) although I havent checked inside yet. it is as deaf as a post on FM.

Someone suggested installing a chinese FM tuner but I would prefer to keep it old school.

There is an official Eddystone mod involving a OC171 transistor, which is what I am talking about. I think it simply adds gain into the IF stage.

bc312 · 6th Jan 2020, 4:29 pm

Before looking at modifications, check out the attached link to a restoration article on the EUG website by Gerry O'Hara. The problem with your EB35 may be related to the troublesome OC171/AF117 germanium transistors - easily resolved by fitting a transistor(s) from the AF12x range.

http://eddystoneusergroup.org.uk/Res...EB35%20MkI.pdf

I have an EB35 MkII/S and this required most of the OC171/AF11x transistors being replaced.

Mike

Argus25 · 7th Jan 2020, 10:19 am

The EB35 is fine as it is, does not require in mod for increased sensitivity or increased performance. The problem is twofold, 1) a proper alignment and 2) the elimination of the OC171 transistors.

By far and away the better replacement transistor is the AF178 (I still think these are available at Langrex and other places).

Replace all of them. Check all the electrolytics, replace as required.

Then perform an alignment with a suitable RF generator and the set will surpass your wildest expectations. I have two EB35's and with AF178's fitted and with alignment the performance is outstanding.

You can use AF127 etc, but the lead wires are more difficult and they don't really look the part.

Another great transistor with long lead wires as a replacement for OC171/AF117 etc is the 2N2084. Unfortunately most stocks of this have sold out now.

crestavega · 4th Jul 2020, 3:39 pm

Finally figured out why my EB35 was so very deaf on FM. the FM module power supply appears to have been mis-wired by some previous fiddler.
(see my spot-the-difference photo)

corrected the wiring to the FM module and the FM performance is just about adequate.

Comments noted regarding changing out all OC171's for AF12x and I may well do this however:
in discussion with a fellow enthusiast, it was suggested that I redesign the IF for FET's.
has anyone done anything like this?

6th Jan 2020, 2:03 pm	#1
crestavega Pentode Join Date: Apr 2014 Location: Kirkwall, Orkney, UK. Posts: 165	Eddystone EB35. FM mod. Has anyone got any practical experience of the FM IF mod on the EB35 Mk1? 'Ive acquired one, which I assume to be original (ie, unmodded) although I havent checked inside yet. it is as deaf as a post on FM. Someone suggested installing a chinese FM tuner but I would prefer to keep it old school. There is an official Eddystone mod involving a OC171 transistor, which is what I am talking about. I think it simply adds gain into the IF stage.

6th Jan 2020, 4:29 pm	#2
bc312 Pentode Join Date: Feb 2005 Location: Longfield, Kent, UK. Posts: 240	Re: Eddystone EB35. FM mod. Before looking at modifications, check out the attached link to a restoration article on the EUG website by Gerry O'Hara. The problem with your EB35 may be related to the troublesome OC171/AF117 germanium transistors - easily resolved by fitting a transistor(s) from the AF12x range. http://eddystoneusergroup.org.uk/Res...EB35%20MkI.pdf I have an EB35 MkII/S and this required most of the OC171/AF11x transistors being replaced. Mike __________________ Leave me alone - I know what I'm doing. BVWS member, EUG, G-QRP Radio Bygones/Radiophile

7th Jan 2020, 10:19 am	#3
Argus25 No Longer a Member Join Date: Oct 2016 Location: Maroochydore, Queensland, Australia. Posts: 2,679	Re: Eddystone EB35. FM mod. The EB35 is fine as it is, does not require in mod for increased sensitivity or increased performance. The problem is twofold, 1) a proper alignment and 2) the elimination of the OC171 transistors. By far and away the better replacement transistor is the AF178 (I still think these are available at Langrex and other places). Replace all of them. Check all the electrolytics, replace as required. Then perform an alignment with a suitable RF generator and the set will surpass your wildest expectations. I have two EB35's and with AF178's fitted and with alignment the performance is outstanding. You can use AF127 etc, but the lead wires are more difficult and they don't really look the part. Another great transistor with long lead wires as a replacement for OC171/AF117 etc is the 2N2084. Unfortunately most stocks of this have sold out now.

4th Jul 2020, 3:39 pm	#4
crestavega Pentode Join Date: Apr 2014 Location: Kirkwall, Orkney, UK. Posts: 165	Re: Eddystone EB35. FM mod. Finally figured out why my EB35 was so very deaf on FM. the FM module power supply appears to have been mis-wired by some previous fiddler. (see my spot-the-difference photo) corrected the wiring to the FM module and the FM performance is just about adequate. Comments noted regarding changing out all OC171's for AF12x and I may well do this however: in discussion with a fellow enthusiast, it was suggested that I redesign the IF for FET's. has anyone done anything like this? Attached Thumbnails